The present invention relates to a system and a method for providing cellular mobility within a telecommunications system comprising a single exchange, e.g. a Private Branch Exchange or a private telecommunications Network Exchange or a private network with a number of exchanges.
The invention further relates to an arrangement for providing a mobile cellular telephone with access to an exchange and particularly to the services provided by the exchange substantially in the same way as a cordless telephone within radio coverage of a radio exchange adjunct to the exchange. The invention also relates to mobile telecommunications system comprising a cellular communication system and a private network wherein cellular access is provided to the private network and to the services offered thereby.
In a system known today a cordless user who is within radio coverage of a radio exchange which is adjunct to a private branch exchange has access to the services offered by the private branch exchange. If however the user is not within radio coverage of a radio switch adjunct to the private branch exchange, a cellular phone has to be used. With the cellular phone it is however not possible to access the services offered by the private branch exchange other than those provided to an ordinary analogue telephone or a so called POTS phone (plain old telephone service) over the public network.
A number of attempts have been done to provide access to both cellular communication networks and private networks or to interconnect the networks. Through using combined telephones, i.e. a cellular telephone and a cordless telephone in one which comprises double equipments of transceivers, antennas etc. with which it is possible to change between a cellular network and the private network. In other systems a user is required to have two different telephones one for the cellular network and one for the private network. None of the systems provide cellular access to the private network or to the services provided by a PBX or a private network. A combined telephone as referred to above is quite a complicated device and there is also no cellular access provided to the services offered by the private network.
In another system illustrated in EP-A-462 727 a mobile communications network is illustrated comprising a PCN-network and a private automatic branch exchange (PABX) connected thereto. Calls which involve mobile subscribers associated with the PABX are routed via a base station controller comprising a mobile services switching center functionality of the PCN-network. A private protocol of the PABX is used. This requires that there are specific protocols in the PABX which means that it is not possible to use the exchange as it is but it has to be modified. Moreover, it is not possible through this arrangement to get access to all services provided by the private branch exchange or the private network and for example the same telephone number can not be used but an additional numbering plan has to be used for this particular category of users.
Also with this known system it is not possible for a cellular phone to get access to all the services provided by a PBX or a private network and particularly it is not possible to use the same numbering plan irrespective of whether using a cellular or a cordless phone.